In underground coal mining, consolidation and sealing of geological and artificially deposited rock and earth formations are carried out to a very large extent with polyurethane systems, see:
Journal: Gluckauf (1968), pages 666-670;
Journal: Gluckauf (1977), pages 707-711;
Journal: Bergbau (1977), pages 124-129;
German Pat. No. 1,758,185;
German Pat. No. 1,784,458.
Two component polyurethane systems are generally forced under pressure into the formations which are required to be consolidated. The starting components used for these systems are generally commercial polyisocyanates and polyols having a molecular weight from 400 to 600 and a hydroxyl number of 350 to 400. According to German Pat. No. 2,436,029, the polyols are rendered flexible with polyols having a hydroxyl number from 50 to 90 and a molecular weight from 2,000 to 35,000.
Natural limits to the possibilities of using polyurethane are given by rock formations which carry water since water destroys the polyisocyanate and thereby significantly interferes with the stoichiometric proportions of the reactants. In addition, water and polyisocyanates preferentially react to form polyureas whch do not adhere to the cracks and fissures in the rock. Warnings are always given that in consolidation work carried out with polyurethanes, water must be kept away from the zones of rock which are required to be consolidated. See Gluckauf (Journal) (1972), pages 10 to 13.
One fundamental disadvantage of using polyurethanes in coal mining is that the hardened product is readily combustible. When substantial quantities of hardened polyurethanes are situated in fissures in the coal, fire due to spontaneous ignition of coal is liable to be spread by polyurethanes. Attempts have therefore been made to overcome the disadvantages of polyurethane by using systems which are virtually incombustible and obtainable in an aqueous form so that consolidation may also be carried out in moist or wet formations.
Extensive experiments, for example, have been carried out with aqueous formaldehyde-urea solutions. Sufficient consolidation could, however, not be achieved with these systems because the products obtained undergo severe shrinkage during the hardening process.
Attempts have also been made to use water glass solutions for consolidation. The hardening of water glass solutions requires the addition of hardeners. Acids and substances which give rise to acids such as phosphoric acid, sulphonic acid, esters, e.g. glycerol triacetate, ethyl acetate and other organic substances, such as formamide and glyoxal are used for this purpose. Calcium chloride, aluminum sulphate, magnesium chloride, magnesium sulphate, aluminum chloride and silicofluorides have also been used as hardeners.
Although relatively coarse sand and gravel can be consolidated to a certain extent by these processes, e.g. for the purpose of consolidating building sites, a high degree of consolidation cannot be achieved because the hardening of water glass is accomplished by a considerable volumetric shrinkage so that the composite mass produced becomes detached from the surfaces of the cracks and fissures.
The present invention solves the problem of providing a process for the consolidation and sealing of geological and artificially deposited rock and earth formations which obviates the disadvantages described above of the known consolidation processes and achieves satisfactory strength values as well as being resistant to moisture and non-combustible.
According to the invention, this problem is solved by mixing intimately polyisocyanate with water glass solutions and leaving the resulting emulsion to harden in the formation which is required to be consolidated. The solid masses which form have excellent adherence to dry and wet geological formations, particularly since the shrinkage which normally occurs when water glass solutions are hardened without the addition of polyisocyanates is completely absent and instead, the bond is strengthened by a certain increase in volume during hardening. One special advantage of coal mining is that the hardened consolidating agent is non-inflammable and the composite mass which forms in the gaps and cracks and the like is of great strength which is highly advantageous for stabilizing the formation.
It is surprisingly found that hardened composite masses also adhere to fatty coal such as coal which has a relatively high bitumen content, so that excellent consolidation is obtained for every type of coal.